Evaluation of multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) for sulfur metabolic studies using 34S-labelled yeast

A multi-collector ICP-MS instrument was evaluated for the on-line measurement of sulfur isotope ratios during the liquid chromatographic separation of sulfur metabolites in mouse urine after the oral administration of 34S-labelled yeast. The multi-collector instrument used was equipped with both Faraday cups and ion counters at positions L4 (32), C (33) and H4 (34). For the optimisation of the resolution, cup configuration and measurement conditions an artificial mixture of natural sulfur and highly enriched 33S and 34S was prepared. The results were compared with those obtained using a sector field single collector instrument from the same manufacturer. Both instruments provided good accuracy in the measurement of sulfur isotope ratios but better precision (<0.01%) was obtained with the multi-collector instrument. For HPLC coupling a nebulization–desolvation system (Aridus II) was used to eliminate the high amounts of methanol present in the mobile phases and maintain the sensitivity for sulfur during the gradient separation of urinary metabolites. Preliminary sulfur metabolism studies were carried out feeding healthy mice and mice with prostate cancer with one dose of yeast enriched with 34S and measuring the sulfur metabolites in urine at different times using a 33S solution as a post-column spike. Chromatograms obtained showed different sulfur isotope enrichments for several metabolites in healthy and diseased mice. However, the variability in retention times from sample to sample hindered the interpretation of the results. Additionally, the number of samples is not enough to draw any metabolic conclusions at this stage.